Preheat the oven to 200ºC, fan 180ºC, gas 6. Put the sausagemeat in a bowl with the semi-dried tomatoes, spring onions, parsley, lemon zest, breadcrumbs and a good grinding of black pepper. Mix together with a wooden spoon, or with your hands, until well combined.
Cut the pastry block in half and, on a lightly floured surface, roll out 1 piece to make a long rectangle shape, measuring about 40cm x 15cm, with a thickness of about 3mm. Form half the filling into a log about the length of the pastry. Put the sausage log on the pastry about 5mm in from the edge of the pastry.
Brush the edge with the beaten egg, then fold the pastry over the sausage filling and press to seal the edge - you could crimp using your fingers or press down with a fork. Cut into 6 rolls. Prepare a second batch using the remaining pastry and filling.
Mix together the sesame seeds and poppy seeds. Using a sharp knife, make a slit in the top of each sausage roll, then brush with beaten egg and sprinkle with the seeds. Bake for 20 minutes until golden and risen. Remove from the oven and cool slightly on a wire rack.
Cook's tip: you can make the sausage rolls the day before, up to the end of step 3, then put them in the fridge overnight. When you're ready to bake them, continue from step 4.